You should be able to check your local hunting/camping/sporting goods stores for emergency outdoor "space" blankets
These are the aluminized (usually silver) mylar blankets, fairly thin, suitable for streamers or chutes, usually only cost a couple bucks. The blankets are something like 6 ft x 8 and should give you enough material to work with
And BTW, there is nothing sacred about mylar. If you can find a big enough piece of "Dura-Lar" (I don't know what that is) to make your streamer, give it a try
In dog beers, I've only had one....